Hopf-type intermediate-scale bifurcation in single-stage power-factor-correction power supplies

This paper reports intermediate-scale instability in a single-stage power-factor-correction (PFC) power supply that employs a cascade configuration of a boost stage operating in discontinuous conduction mode (DCM) and a forward stage operating in continuous conduction mode (CCM). The two stages combine into a single stage by sharing one main switch and one control loop to achieve input PFC and tight output regulation. Main results are given by "exact" cycle-by-cycle circuit simulations. The intermediate-scale instability usually manifests itself as local oscillations within a line cycle. Based on the stability analysis of a buck converter operating in CCM, the underlying mechanism of such instability can be attributed to the Hopf bifurcation occurred in CCM forward stage. Finally, experimental results are presented for verification purposes.